Exam 2 Notes- Laura

Genetic mapping is essential in genetic research to identify and isolate new genes.
It helps discover genes linked to hereditary diseases.
Gene sequence alone does not indicate gene function.
Genetic markers can test for diseases and link to associated genes.

Linkage: Genes that are transmitted together more often than by chance.
- Genes may be linked on a chromosome.
- Finding a gene associated with a genetic disease can further our understanding of inheritance patterns and gene interactions.
Homologous Chromosomes: Different alleles of genes reside on these chromosomes.
- Example with three genes: A, B, C.
- No crossing over between A and B implies they are closely linked.
The proximity of genes affects recombination rates; if genes are further apart, they are less likely to be linked.

Recombination frequency provides insights into the distance between genes on a chromosome.
The likelihood of crossing over is a measurement of genetic distance.
If the rate of recombination is lower than 50%, the genes are linked.
- A 50% rate of recombination would indicate independent assortment, with genes inherited together only half the time.

Count offspring's genotypes; for example, from 226 offspring:
- 102 parental types, 114 recombinant types.
Calculate recombination frequency: recombinants (202) / total offspring (335) = 33.5%.
Genes with a recombination frequency lower than 50% are closer than expected.

Heterochromatin: Tightly coiled, contains noncoding DNA sequences, has fewer genes (e.g., telomeres, centromeres), crosses over less due to compactness.
Euchromatin: Loosely coiled DNA where more crossing over occurs and coding regions are located.

Recombination frequency indicates genetic distance; can be expressed in percentage, map units, or centimorgans.

Double Crossover: Yields no recombinants.
Three-point cross: Necessary for mapping more than 2 genes; gives better visibility of gene distribution and crossing over.
- Nonrecombinants are the most frequent result, and the maximum recombination rate cannot exceed 50%.
Probability of simultaneous exchanges in double crossovers is lower than single events; double crossover gametes are the least frequent type.

Polymorphic markers signify genetic variability, vital for comparison in genetic studies.
Humans differ by roughly 1 in 1000 base pairs in their genomes.
Types of Polymorphisms:
- SNP (Single Nucleotide Polymorphism): Single nucleotide changes, numerous in human genomes; significant in disease association.
- RFLP (Restriction Fragment Length Polymorphism): Detects variations by cutting DNA at specific sequences.
- SSR (Simple Sequence Repeats): Tandem repeats useful in genetic mapping; vary in changes of repeated sequences among individuals.
- CNV (Copy Number Variation): Large duplications or deletions in the genome impacting gene dosage and expression.

Genetic mapping aids in understanding disease genetics and human population history.
Can be utilized in plant and animal breeding, conservation efforts, and evolutionary studies.

Sugar-Phosphate Backbone: Formed through phosphodiester bonds.
Hydrogen Bonds: Between nitrogenous bases; A pairs with T, G pairs with C.
DNA Replication: Semi-conservative mechanism where each strand acts as a template, characterized by the replication fork.

Helicase: Unwinds DNA strands.
Gyrase/Topoisomerase: Relieves torsional strain during unwinding.
Single-Stranded Binding Proteins (SSBs): Stabilize unwound DNA strands.
Primase: Synthesizes an RNA primer necessary for DNA polymerase action.
DNA Polymerase: Synthesizes new DNA strands by adding nucleotides in a 5' to 3' direction.
DNA Ligase: Joins Okazaki fragments on lagging strand and seals breaks in the DNA.

Telomeres shorten with each cell division due to the inability to fully replicate the ends of linear DNA.
Telomerase: Extends telomeres by synthesizing sequences complementary to telomeric DNA; often reactivated in cancer cells to maintain cell division capability.

Restriction Enzymes: Molecular tools for gene cloning and DNA manipulation; cut at specific sequences producing fragments for recombinant DNA technologies.
PCR (Polymerase Chain Reaction): Amplifies specific DNA sequences.
Next Generation Sequencing: High-throughput sequencing technologies that analyze many DNA fragments rapidly and accurately.
Transformation and Gene Transfer: Incorporation of foreign DNA into bacterial plasmids for various applications, including treatment for diseases and enhancement of agricultural crops.